Coronary heart disease is the leading cause of death worldwide, and is primarily attributable to the detrimental effects of tissue infarct after an ischemic insult, The most effective therapeutic intervention for reducing infarct size associated with myocardial ischemia injury is timely and effective reperfusion of blood flow back to the ischemic heart tissue. However, the reperfusion of blood itself can induce additional cardiomyocyte death that can account for up to 50% of the final infarction size. Currently, there are no effective clinical pharmacologic treatments to limit myocardial ischemia/reperfusion (MI/R) injury in heart attack patients. Reperfusion injury is initiated by decreased endothelial derived nitric oxide (NO) which occurs within 5 min of reperfusion, and may in part be explained by PKC ßII mediated activation of NADPH oxidase, which occurs upon cytokine release during MI/. PKC ßII activity is increased in animal models of MI/R and known to exacerbate tissue injury. PKC ßII is known to increase NADPH oxidase activity in leukocytes, endothelial cells and cardiac myocytes via phox47 phosphorylation, and decrease endothelial NO synthase (eNOS) activity via phosphorylation of Thr 495. NADPH oxidase produces superoxide (SO) and quenches endothelial derived NO in cardiac endothelial cells. Moreover, PKC ßII phosphorylation of p66Shc at Ser 36 leads to increased mitochondrial reactive active oxygen species (ROS) production, opening of the mitochondrial permeability transition pore (MPTP), and pro-apoptotic factors leading to cell death and increased infarct size. Therefore, using a pharmacologic agent that inhibits the rapid release of PKC ßII mediated ROS, would attenuate endothelial dysfunction and downstream pro apoptotic pathways when given during reperfusion and should be an ideal candidate to attenuate MI/R injury. PKC ßII peptide inhibitor mechanism of action is to inhibit PKC ßII translocation to cellular substrates such as eNOS, NADPH oxidase, and mitochondrial p66Shc protein that increase ROS leading to opening of the MPTP which in turn leads to consequent release of proapoptotic factors into the cytosol. We've previously shown that PKC ßII peptide inhibitor restored post-reperfused cardiac function and reduced polymorphornuclear leukocyte (PMN) infiltration in isolated rat hearts subjected to MI(20min)/R(45min) reperfused with PMNs. In addition, the use of PKC ßII peptide inhibitor (10-20 µM) correlated with the inhibition of SO release from isolated leukocytes suggesting that this dose range maybe effective in attenuating ROS production. We extended our research in the current study by using a MI (30min)/R (90min) isolated perfused rat heart model. A cell permeable PKC ßII peptide inhibitor (10-20 µM) was given at the beginning of reperfusion for five minutes. Post-reperfused cardiac function and infarct size were measured and compared to untreated control MI/R hearts.

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This article was published in Proceedings of the 24th American Peptide Symposium, December 201.,